P0526

Fan Speed Sensor Circuit

Indicator

The PCM has detected an incorrect amount of voltage (high or low) in the electric cooling fan control circuit.

Code Set Parameters

Voltage variations that vary by greater than 10-percent of the manufacturer’s specified reference voltage will cause a code to be stored and possibly a service engine soon lamp to be illuminated. Some vehicles require multiple drive cycles (usually three) for the service engine soon lamp to be illuminated. If there is a code stored and no service engine soon lamp, the code may be displayed as a pending code.

Symptoms

Symptoms will likely be limited to only service engine soon lamp illumination and a stored code. However, they may also include an overheating engine (when the vehicle is not in motion) and reduced air conditioner efficiency.

Common Causes

Common causes include a bad cooling fan motor or a faulty cooling fan relay. Less common causes include corroded or loose electrical connectors, a faulty engine coolant temperature sensor, and open or shorted electrical wiring (often resulting in a blown fuse).

Common Misdiagnosis

Technicians report the replacement of cooling fan motors without performing a thorough diagnosis results in many unsuccessful repairs. Cooling fan relays have been the subject of several technical service bulletins and recall campaigns in late model vehicles.

Diagnosis

Most late model vehicles utilize a system of one or more electric cooling fans for engine cooling and air conditioner system operation

These fans are categorized as a primary cooling fa and one or more secondary fans

The primary fan is usually referred to as the “Fan 1” and the remaining fans are labeled in sequence (“Fan2” and “Fan 3”)

Single speed engine cooling fans are the most common but several automakers also use electric fans with multiple speed settings

Still other models are equipped with electro-hydraulic engine cooling fans that rely on voltage and hydraulic pressure (usually generated by the power steering pump) to control operation and fan speed.
Several tools will be instrumental in successfully diagnosing this code

A suitable OBD-II scanner (or code reader) and a digital volt/ohmmeter will be most helpful in performing a successful diagnosis

Always retest the system after repairs are completed to ensure success.
If all system wiring, connectors, and components (Including fuses) appear to be in normal working order, connect the scanner (or code reader) to the diagnostic connector and record all stored codes and freeze frame data

This information can be extremely helpful in diagnosing intermittent conditions that may have contributed to this code being stored

Continue by clearing the code and operating the vehicle to see if it returns

This will help to determine whether or not the malfunction is intermittent

After the codes are cleared, test drive the vehicle to see if the code returns

If the code fails to immediately return, you may have an intermittent condition

Intermittent conditions can prove to be quite a challenge to diagnose and in extreme cases may have to be allowed to worsen before a correct diagnosis can be made

All of these engine cooling fan systems are primarily controlled by the PCM, which uses input data received from the engine coolant temperature sensor to calculate fan activation and/or speed

When the engine reached a predetermined temperature (225-degrees Fahrenheit is most common), the PCM provides a voltage signal to the fan relay

The fan relay is supplied with a constant supply of fused voltage, as well as one or more ground signals and the PCM signal (which may also be a ground signal)

The engine cooling fan relay/s help to transform a low voltage (or ground) signal from the PCM into the battery level voltage signal required to operate the cooling fan motor

By using a scanner to activate the engine cooling fan, and carefully performing a quick voltage and ground test (battery voltage is normal) at the cooling fan motor, you may successfully determine whether the fan motor is faulty or a lack of voltage/ground is the culprit.
If no voltage is present at the primary cooling fan motor, begin by testing the system fuses

If all of the fuses are good, locate the engine cooling fan relay and compare voltage readings at the connector to the manufacturer’s specifications for fan operation

Replace or repair relays, fuses, or open/shorted circuitry as required

If there is no output signal from the PCM, connect a suitable scanner and observe engine temperature

If engine temperature readings are not within manufacturer’s specifications, suspect a faulty engine coolant temperature sensor

Test the sensor by comparing actual temperature to resistance values with the manufacturer’s specified temperature to resistance values

If temperature to resistance values fail to coincide, then replace the engine coolant temperature sensor

Most models use one engine coolant temperature sensor for engine drivability and another for temperature gauge operation.
If disconnecting the engine coolant temperature sensor connector yields no change in the engine temperature reading displayed on the scanner, suspect shorted or open wiring or electrical connectors in the cooling fan circuit

PCM failure is rare but possible.
Secondary engine cooling fans are a little more complex in operation

Secondary engine cooling fans are usually controlled by dual systems

Secondary fans located on the engine side of the radiator are often responsible for assisting with cooling the engine, as well as providing air flow for the air conditioning condenser

Secondary fans located on the opposite side of the radiator from the engine are usually dedicated to providing air flow for the a/c condenser, only

Electric condenser fans are also activated by the PCM, but instead of relying upon an input signal from the engine coolant temperature sensor, it uses a signal from a pressure sensor that is normally located in (or on) a pressurized component of the air conditioning system

As the air conditioning compressor begins to operate, and pressure increases in the a/c system, an electrical circuit in the pressure switch is completed

This process supplies the PCM with a signal

The PCM in turn, sends a voltage (or ground) signal to the fan relay which transfers the low voltage (or ground signal) to a battery voltage signal, which is required for fan operation

Cooling fans that are used for a dual purpose (engine cooling and a/c condenser air flow) are activated by either the engine coolant temperature sensor signal and/or the a/c pressure signal (both via the PCM)

Test secondary cooling fan operation and circuitry in much the same manner as you would the primary cooling fan

Replace components and repair circuitry as needed.
Multi-speed cooling fan motors are monitored by the PCM for precise RPM levels

Fans that spin too rapidly, or too slowly, will trigger a stored code and a service engine soon lamp

These types of systems typically utilize a system of resistors to regulate voltage and vary fan speed

Obtaining a fan RPM to voltage conversion chart for your vehicle will be instrumental in determining the cause of a fan overspeed or underspeed condition